Not trying to brag, but I've probably got more time and effort in brake development and in making a fast ITS car with solid discus up front, rear drums actually work. Here's what I've learned over the years after a lot of trying various things. First, note that my front discs (Triumph TR8, 2011 SARRC champion) are slightly smaller than a Z cars, and the pads the same, slightly smaller. Rear drums are about the same size as are the shoes, but your drums are ally while mine are heavy metal. So, onto my experience:
1. You MUST get the rears to work for the fronts to have a chance of surviving at CMP, Road Atlanta or VIR. To do that, you simply must you race shoes and right now, in my view, there is only one option: Porterfield's new race compound (LS something I think). R4 does not work. You need LS and it's magic. Good friction coefficient, and it lasts. I'm on season two of my FIRST set of shoes and the shoes still look good, and the rears work.
R4 can't handle the heat. Carbotech has discontinued their race shoe material while trying to solve the swelling issue, which was terrible. Shoes would swell on the first use so bad that the car would not roll. Would create enough drag to cause a measurable 10 hp loss on the dyno. I love the Carbotech guys but that material sucks.
Porterfield went all out to help the burgeoning vintage scene and this new compound they have is awesome. Handles heat, no swell.
2. You must duct the rears. I think the main reason is to keep the wheel cylinder alive. I've seen it happen to Z cars and to my car, the cylinder gets crusty hot and just disintegrates. Hell, I've seen fires on Z cars from this happening. You can't cut holes in the body to get air to the drums, so I just drill the backing plates for "exit" and then add a three inch duct to the backing plate and run a hose under the body of the car. It's not ideal but it gets some air to them and I've not had a wheel cylinder failure since I did this.
3. Pad choice for the fronts is crucial. After trying everythign under the sun, I've settled on Raybestos ST-43s. Wear hard. Don't kill rotors. Can handle heat and keep stopping. Expensive though, $275 a pop. But last much longer than the Blues and HT-10s I was using before. I've never had much luck with Carbotech on the front although I love the guys. Have a pair of Ferodo FS3000s thta I've not tried but will report when I do. Still, hard to see it being any better than the ST-43s (do NOT get the 41s...they generate too much heat).
4. Get a good duct to the rotor. Make it as straight (the duct) as possible, and have the intake as close to the centerline of the car as possible. Caliper ducts can't hurt but in my experience they don't help much either. Coating the back of the pads iwth heat treatment will make the caliper seals last longer (I generally go a half season now without changing calipers).
5. Use SRF. $70 a bottle that you use once in a season is still better than a $20 bottle that you have use 4 of due to boiling and bleeding fluids.
NC Region
1980 ITS Triumph TR8
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